Drifter-based velocity statistics in the vicinity of the Azores Front
Brown, John E. M.
Paduan, Jeffrey D.
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Surface velocity observations from the Canary Basin of the northeast Atlantic Ocean are studied with emphasis on the region of the Azores Current. Data are based on trajectories of 155 WOCE-standard Lagrangian surface drifters drogued at 15 m depth. Over 52,000 daily velocity estimates are available for the region 45 deg W, 25 deg N and 5 deg W, 45 deg N for July 1991 through March 1995. A clear view of the mean Azores Current emerges around 34 deg N with average speeds of approx. 10 cm/s and eddy kinetic energy approx. 181/sq cm/s2. The Current moves eastward beyond Madeira Island to join the southwestward flowing Canary Current. Part of the flow bifurcates west of the Madeira Plateau around 23 deg W. Eddy kinetic energy in the Canary Current region is only approx. 80/sq cm/s2 even though mean speeds are similar to those in the Azores Current. Zonal averages of the flow show significant convergence in the meridional velocity north of the Azores Front. A time history of the frontal locations is developed based on SST and drifter information. A methodology is presented for converting drifter observations into along-front and cross-front coordinates. Although these frontal locations do not faithfully track the location of the main subsurface front, particularly in the eastern portion of the domain, mean velocities in frontal coordinates support the hypothesis that large-scale subduction of surface waters in this region is concentrated in a region of convergence associated with the Azores Front, particularly from the north.
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